Refractometer Query

[Barge]

G'day All,

I know we're all beer brewers here but I'm having a technical problem I'm hoping for some help with.

I've started making wine at work....

before we get carried away, I work at a High School...and it's part of the course.

Anyhow,

we made a red wine with an O.G. of 1.094 and it stopped fermenting at 0.994. I took a refractometer reading (after calibrating with distilled water) which was 8.15 Brix (after temperature correction).

My problem is that, using various calculators (BeerSmith, and online one posted on AHB) i get different conversions to S.G. from the Brix reading.

For example, the straight conversion of 8.15 Brix is ~1.032 S.G. Using the O.G. reading and the Brix reading gives a corrected S.G. of 0.994, which matches my hydrometer reading.

Can anyone explain how this works? Why do you need the O.G. and the Brix to get the corrected S.G. reading?

Cheers,
Barge

 

[PostModern]

Can anyone explain how this works? Why do you need the O.G. and the Brix to get the corrected S.G. reading?

Alcohol effects refraction.

 

[Guest Lurker]

Alcohol effects refraction.

..and it also affects density.

At the start you had water plus sugar. The sugar increased the density, which you could read with a hydrometer, it also changed the refractive index, which you could measure with your refractometer.

By the end of fermentation you had water, plus less sugar than before, plus alcohol. The sugar still increases the density, and changes the RI, but the alcohol decreases the density and also changes the RI.

From your hydrometer readings, you have apparently fermented 107% of the sugar, to get to a density below 1.0. But that apparent calculation doesnt include the effect of alcohol lowering the density. In reality about 88% of the sugar was fermented.

 

[PostModern]

Good point, GL, the reading that is skewed by the alcohol is the hydrometer reading, not the refractometer reading.

 

[bakkerman]

I've been reading up on this and I have found that refractometers offer no reliable readings once fermentation has set in.

You would need to know the alcohol content to recalibrate the refractometer, thus ending up in a catch 22.
There a recalculation option in Promash that might help.

 

[Barge]

There a recalculation option in Promash that might help.

I use BeerSmith, so no help there.

In reality about 88% of the sugar was fermented.

So the refractometer is measuring the residual sugar left in solution?

 

[AndrewQLD]

I use BeerSmith, so no help there.
So the refractometer is measuring the residual sugar left in solution?

Why don't you use the refractometer tool in beersmith, it calculates unfermented wort, fermenting wort and finished beer.

Cheers
Andrew

 

[Barge]

I used that tool, plus some others, and get the right result...just trying to work out what's going on, as much to be able to explain to a class of 20 kids why what they're doing works, instead of saying "just do it"

GL's post was very informative - just double checking that the brix reading at the end of fermentation gives the amount of residual sugar. If that's the case, the effect of alcohol on the RI of the solution doesn't affect the refractometer. I'm bloody confused.

 

[AndrewQLD]

Maybe this article will help refract

I also have a guide of sorts that I will post shortly, once I find it.

Cheers
Andrew

 

[AndrewQLD]

Found it, I really need to sort all my brewing files one day.
Don't know if it is any use, but there is some info in there.

View attachment Misco_Wine_Refractometers.pdf

Cheers
Andrew

Edit: forgot to mention it came from here Misco

 

[Darren]

My understanding is that ATO use a hydrometer to assess alcohol levels for excise purposes. If that is the case then one could presume that refractometer is useless post-ferment.
Comments welcome

cheers

Darren

 

[Ross]

My understanding is that ATO use a hydrometer to assess alcohol levels for excise purposes. If that is the case then one could presume that refractometer is useless post-ferment.
Comments welcome

cheers

Darren

:blink:

That's like saying, if they happened to use a refractometer, then a hydrometer is useless...

 

[GMK]

Promash has a formulae where you enter the refractometer reading Prior to fermentation + the final refrac reading.
It calculates it all out making allowance for the alcohol present.

Hope this helps

 

[Darren]

Too many variables to accurately calculate alcohol content. Promash formulae is just there to give an indication because HBers requested it.


Ross, if the refract is soooo much easier. Why do ATO not use it?

cheers

Darren

 

[Ross]

Too many variables to accurately calculate alcohol content. Promash formulae is just there to give an indication because HBers requested it.
Ross, if the refract is soooo much easier. Why do ATO not use it?

cheers

Darren

Refractometers aren't useless, but a narrow range hydrometer is more accurate & easier. No need for complicated formuleas & trying to read dark beer samples. Hence using a hydrometer, makes heaps of sense from an ATO perspective. Likewise, I prefer using a hydrometer for post ferment readings - & you get to taste test as well

cheers Ross

 

[blackbock]

I reckon the ATO would use whatever method leads to the highest tax... ;-)

 

[Keith the Beer Guy]

Hi Barge,

heres the simple version.

Some stuff bends light, the amount the light gets bent has got something to do with the refractive index of the stuff you are looking at.

If you have more of your stuff, say sugar in your wort for instance, the light gets bent more. So the more sugar to start with the higher the Brix value.

Fermentation happens. The amount of sugar get less. This lowers the Brix value.

But wait! You have made some new stuff - this stuff is called alochol. Now it turns out alcohol doesn't have the same RI as sugar and so it bends the light a different amount.

So when you measure the Brix value the reading is all buggered up.

But because the alcohol came from the sugar in the first palce you can correct the Brix reading to get a true value for the final gravity or alcohol.

Hope this is clear enough.

Happy fermenting,

Keith

 

[Darren]

I reckon the ATO would use whatever method leads to the highest tax... ;-)

BB,

Probably right. I suspect they use the measure that conforms to a standard and gives the same result no matter what the composition of the starting sugar.

cheers

Darren

Refracto for the start of ferment. Hydro for the finish.

Otherwise you might as well make up a number

 

[goatherder]

I've given up on my refractometer - not happy with the reproducibility. I use the hydro - it works the same every time plus you can drink the sample.

 

[Barge]

Keith,

Makes perfect sense...cheers mate. You'd think a chemistry degree would help me with that, but i always was ordinary at physics.

Cheers for the pdf Andrew...i'll have a read at work on monday.